1. Field of the Invention
The present invention is directed to a carrier substrate with a resistor track for an electrical device in which a slider for providing the connection with electrical energy is movable along the resistor track and the resistor track comprises numerous metal strips which are aligned transversely with respect to the main direction in which said resistor track extends. These elements are located at a distance from one another and are interconnected on one side by a defined, electrical resistor, in particular for a potentiometer of a lever sensor for the level indication in a fuel tank.
2. Description of the Related Art
Carrier substrates of the above type are used for level sensors in fuel tanks of modem motor vehicles and are therefore generally known. There are, however, numerous other applications for which electrical energy also has to be picked up from a resistor track by means of a slider and fed to a moving component.
In the case of level sensors, the aim is usually to achieve linearity between the filling level and the displacement of the level-indicating indicator. Since, however, the cross section of tanks in which the filling level is measured often varies considerably over the height of the tank, in order to adapt to spatial conditions of the motor vehicle, producing this linearity requires sophisticated calibration. In the case of the level sensors known thus far, the individual metal strips are interconnected on one side by a resistor surface bridging them. For changing the resistance of the resistor track, the resistor surface between the metal strips is cut into radially to differing extents, so that the electric current has to flow over a more or less wide remaining width of the resistor surface from one metal strip to the other. The cutting into the resistor surface is currently carried out by means of laser light. If it is desired to use this technique to calibtrate a level sensor in such a way that a linear characteristic is obtained, the number of laser cuts required would be increased by about tenfold, which would mean that a high computer capacity would be required for automatic calibration and that the positioning accuracy of the laser would have to meet undesirably high requirements in order that the tolerances do not accumulate impermissibly from one laser cut to the next.
The invention is based on the problem of developing a carrier substrate with a resistor track which can be calibrated with as little effort as possible in such a way that a linear characteristic can be achieved for the indication of a device operating with such a resistor track.
This problem is solved according to the invention by regions of metal strips having extensions toward one side of the resistor track which are bridged by an adjusting resistor and by the adjusting resistor being designed for isolating resistor regions by cuts running transversely with respect to the extensions.
Such a design makes it possible to isolate resistor regions with relatively little effort and, as a result, change the electrical resistance in the respectively chosen regions specifically for the entire region, by isolating more or less wide resistor regions. Since the calibration takes place in the region of the extensions, the calibrating regions can be arranged on the printed circuit board without any problem and do not influence the movements of the slider.
It is particularly cost-effective if the adjusting resistor is produced on the extensions by printing thereon and the cuts are formed by means of laser light.
The calibration can be carried out by isolating previously defined individual resistors in fixed calibrating steps and therefore with particularly little computer effort if the adjusting resistor comprises a plurality of resistor tracks running transversely with respect to the extensions.
However, stepless calibration is also possible if, according to another development of the invention, the adjusting resistor forms a closed surface printed onto the extensions.